Making gear sprocket pinion

[atunguyd]

Wanted to ask the opinions of the experts here.

My son has an electric skateboard which we built together. It is belt driven but the hdt 3M belt has stripped pretty quickly so I am thinking of replacing this with a chain drive.

I have ordered a the sprocket (that mates with one wheel), chain and pinion set but the gear ratio of 14:27 is going to be a bit high (belt was 1:3). I cannot increase the the size of the wheel sprocket as it will end up being bigger than the wheel so I am thinking I need to reduce the size of the motor pinion to something like a 9 tooth pinion.

The chain is a 25H which is a US standard I believe so I am not going to get a pinion locally here and our postal thieves, I mean service, is unreliable.
I am thinking that it must be possible to just make one out of round bar.

Can anyone advise on the best way to do this?
I found the following video which had impressive results considering he did not use machine tools
https://youtu.be/t_g_sY0ZAmI
I am thinking that unless someone advises a better method I may do something similar but use the the mill to drill the circle pattern and use the lathe to do most of the other cutting (probably only use the grinder to sharpen the sprocket teeth).

Is this the way to go out is there something I am missing?

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[liveaboard]

I doubt the sprocket made in that vid lasted for more than a few hours.

You need real accuracy with the hole positions, so that the load is spread over several teeth.
And it has to be hardened or there's no hope for a small driving sprocket.

I've worked with chains and belts, I prefer belts now. But you need one rated for the load.

Let us know how it goes.

[atunguyd]

Agreed Liveaboard and that is why I am proposing that i drill those holes on the mill using either the DRO hole pattern feature or the rotary table.

For the intended application here the when sprocket gets bolted to the back of the skateboard wheel - since the wheel is only 73mm in diameter I obviously needs to use a sprocket or pulley (for the belt) that is a lower diameter (otherwise the skateboard will be riding on the pulley and not the wheel). In order to do this and achieve the desired gear ratio of 1:3 I cannot use a 5mm pitch HDT belt. The 3mm pitch one though did not last long before the teeth were stripped from the belt which is why I am thinking of going the chain route.

Would I be correct in saying that the critical dimensions on a roller chain sprocket would be the round holes where the rollers themselves sit, these would need to be the correct radius (or at least slightly greater than then chain roller diameter) and correctly spaced on the pitch diameter of the sprocket. The teeth on the other hand are not as critical as then just need to guide the rollers into their positions?

[liveaboard]

yes, the rollers ride in the grooves; for a small sprocket like that you'll need to taper away the teeth for clearance.
I never made one; I was about to when I discovered a ready made one that would work for me.
I calculated the sprocket as a polygon using simple trig.
So simple, even I could do it.

I haven't worked with the little 3mm belts, but the bigger sizes come in different widths for higher capacity.

Bigger drive wheels not a possibility?

[atunguyd]

Unfortunately bigger wheels are not really an option and on a skatebaord there is a limit anyway.
Also going to a thicker belt might not work as there is limited room behind the wheels and we would need to replace all the pinions too.

We are working on a budget here as this is not just about making the electric skateboard but also to teach my 13 year old a little lesson in financial responsibility. He decided that he wanted an electric skateboard and, like many toys that adults get into, the prices are just crazy. I suggested to him that we can convert his existing skateboard into an electric one using a lot of the radio control parts that I already have and re purposing a Nintendo Wii nunchuck controller as the bluetooth remote. All he had to buy was a brushless motor of the correct spec. He had to do odd jobs to make the money for the motor (not easy in this day and age as kids cant go get a paper route or do odd jobs like that that anymore - seems that adults have taken over that area too but thats a different discussion).

So we have a working electric skateboard however the belt and pulley system we bought from banggood wore out very quickly hence my desire to move to a chain drive. I offered to buy this and it is on its way at the moment, perhaps it will work on the 14:27 gear ratio but I think trying to make a new pinion sprocket with 10 teeth will help us get back to what we had before the belt wore out.

[whateg0]

I think there are programs on the web that will give you a drawing to work from, but the shape of the teeth on a sprocket are fairly easy to draw up, especially in CAD. If I'm doing it from scratch, I start with what I guess would be called the root? That's the semi-circle where the roller rests. After these are done, I draw an arc centered on each and tangent to the adjacent root. That's about all there is to it.

Dave

[10 Wheeler Rob]

Just get one more small sprocket and put a bronze beearing in it for the idler/tensioner. The small sprockets are cheap.

[atunguyd]

Update to this. I found a local supplier that provided me with a 10 tooth pinion, a 31 tooth sprocket and the matching chain (British 04B) at a really good price. machined them to fit onto the wheel and motor and it is all working perfectly tonight.

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